The present invention relates to a video camera technique for automatically following a change of an object in the field of view of a video camera and, more particularly, to such technique for controlling the exposure so as to properly adjust the luminance of the object.
Numerous methods may be employed for controlling the exposure of a video camera. For example, such methods may include an automatic multi-split light measurement exposure control method, an automatic centralized or spot light measurement exposure control method, a manual exposure control method and so forth.
The automatic multi-split light measurement exposure control method utilizes a multi-split light measurement pattern to measure luminance information obtained from picture information. The measured luminance information may be processed to obtain an average value, a distribution, and/or a histogram of such luminance information which may be utilized to control exposure.
The automatic centralized or spot light measurement exposure control method utilizes a light measurement pattern which may be respectively located in or around the center portion of a screen and in a relatively small or spot area in or around such center portion. Luminance information obtained from picture information is measured by use of the light measurement pattern which may be utilized to control exposure.
In the manual exposure control method, an operator or cameraman may determine and/or manually adjust the luminance of an object to be photographed to obtain a desired or acceptable value.
Each of the above-mentioned exposure control methods has disadvantages associated therewith. For example, the automatic multi-split light measurement exposure control method may have difficultly in obtaining a proper exposure of an object in a scene having a relatively large luminance difference between the object and its background (such as in a scene having a backlight or excessive normal light). In such situation, the background information may be incorporated with information of the object to be photographed, thereby making it difficult to obtain a proper exposure of the object. Further, with regard to the automatic centralized or spot light measurement exposure control method, such method may be difficult to use when the object to be photographed is moving. That is, in such method, the operator or cameraman has to photograph the object such that it is always located at the center of a screen. As is to be appreciated, it may be difficult to continuously photograph the object so as to keep it centered on the screen while the object is moving. Furthermore, with regard to the manual exposure control method, an operator may not be able to properly adjust the exposure control in response to a sudden luminance change of an object. Additionally, a problem may arise in that the background may not be set to an optimum luminance level when an object suddenly disappears from a photographing screen.